Effects of Consonant Manner and Vowel Height on Intraoral Pressure and Articulatory Contact at Voicing Offset and Onset for Voiceless Obstruentsa)
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Effects of consonant manner and vowel height on intraoral pressure and articulatory contact at voicing offset and onset for voiceless obstruentsa) Laura L. Koenigb) Haskins Laboratories, 300 George Street, New Haven, Connecticut 06511 and Long Island University, One University Plaza, Brooklyn, New York 11201 Susanne Fuchs Center for General Linguistics (ZAS), Schuetzenstrasse 18, Berlin 10117, Germany Jorge C. Lucero Department of Mathematics, University of Brasilia, Brasilia DF 70910-900, Brazil (Received 13 September 2010; revised 3 February 2011; accepted 12 February 2011) In obstruent consonants, a major constriction in the upper vocal tract yields an increase in intraoral pressure (Pio). Phonation requires that subglottal pressure (Psub) exceed Pio by a threshold value, so as the transglottal pressure reaches the threshold, phonation will cease. This work investigates how Pio levels at phonation offset and onset vary before and after different German voiceless obstruents (stop, fricative, affricates, clusters), and with following high vs low vowels. Articulatory contacts, measured using electropalatography, were recorded simultaneously with Pio to clarify how supra- glottal constrictions affect Pio. Effects of consonant type on phonation thresholds could be explained mainly in terms of the magnitude and timing of vocal-fold abduction. Phonation offset occurred at lower values of Pio before fricative-initial sequences than stop-initial sequences, and onset occurred at higher levels of Pio following the unaspirated stops of clusters compared to frica- tives, affricates, and aspirated stops. The vowel effects were somewhat surprising: High vowels had an inhibitory effect at voicing offset (phonation ceasing at lower values of Pio) in short-duration consonant sequences, but a facilitating effect on phonation onset that was consistent across conso- nantal contexts. The vowel influences appear to reflect a combination of vocal-fold characteristics and vocal-tract impedance. VC 2011 Acoustical Society of America. [DOI: 10.1121/1.3561658] PACS number(s): 43.70.Aj, 43.70.Gr [DAB] Pages: 3233–3244 I. INTRODUCTION nected speech conditions that involve rapidly-varying glottal widths, upper vocal-tract postures, and intraoral pressures. Em- This paper investigates the effects of consonant manner pirical work on consonant voicing, in turn, has mostly assessed and following vowel height on the aerodynamic conditions the timing of phonation or the extent to which an obstruent at voicing offsets and onsets around voiceless obstruents and interval contains voicing (e.g., Docherty, 1992; Lisker and obstruent sequences. Phonation offsets and onsets were Abramson, 1964; Smith, 1997; Stevens et al.,1992; Weismer, determined for eight speakers of German, in six consonantal 1980; Westbury, 1979). Few studies have provided direct aero- contexts (/t/, /S/, clusters /st/, /St/, and affricates =tS=, =ts=) and ^ ^ dynamic and articulatory data about phonation offsets and two vowel contexts (following /A/ vs /i/ or /I/). At the times onsets in consonantal contexts, and those that have mostly of voicing offset and onset, intraoral pressure (P ) was io focused on voiced rather than voiceless obstruents. measured, as was lingua–palatal contact, using electropala- Thus, the general goal of the current work is to help tography (EPG). bridge this gap by quantifying the aerodynamic and supralar- Although voicing has been studied extensively, gaps yngeal conditions at the times of voicing offsets and onsets remain between the empirical data on obstruent voicing and before and after voiceless obstruent consonants produced by theoretical formulations of the physical requirements for pho- multiple speakers, and assessing the likely sources of varia- nation. As detailed in subsequent sections, modeling work has tion across consonants and vowels based on past work. generally focused on phonation thresholds in conditions with Along with providing a better understanding of the general adducted vocal folds and an open vocal tract. Results from relationships between speech articulation and aerodynamics, such studies cannot be straightforwardly extended to con- these data are intended to serve as input for aerodynamic modeling that incorporates vocal-fold abduction and varia- a)Portions of these data were presented at Acoustics 2008, Paris, France, and tions in supraglottal conditions. This paper will focus on the 2010 International Conference on Advances in Laryngeal Biophysiol- group patterns across consonant and vowel contexts. Future ogy/International Conference on Voice Physiology and Biomechanics, work will explore speaker differences and relate the meas- Madison, WI. b)Author to whom correspondence should be addressed. Electronic mail: ured data with simulations obtained via modeling of the lar- [email protected] ynx and upper vocal tract. J. Acoust. Soc. Am. 129 (5), May 2011 0001-4966/2011/129(5)/3233/12/$30.00 VC 2011 Acoustical Society of America 3233 Downloaded 11 May 2011 to 128.36.197.66. Redistribution subject to ASA license or copyright; see http://asadl.org/journals/doc/ASALIB-home/info/terms.jsp A. Modeling of the factors that influence phonation offsets and onsets occur under different aerodynamic condi- tions. In particular, when laryngeal and supralaryngeal fac- 1. Phonation threshold pressures tors are held constant, a higher pressure is needed to initiate The physical requirements for voicing have been quanti- phonation than to maintain it, so that vocal-fold vibration fied for laryngeal models of varying complexity. Ishizaka shows hysteresis (Baer, 1975; Plant et al., 2004). Lucero and Matsudaira (1972) established that sustained phonation (1996, 1999, 2005) established the mathematical nature of in a two-mass model of the vocal folds requires a subglottal this phenomenon as a subcritical Hopf bifurcation and pressure exceeding a threshold value. Titze (1988) extended showed that hysteresis results from non-linear aerodynamic this line of inquiry to the body–cover model of the vocal damping within the vocal folds. In these models, the thresh- folds and provided the following formula for the phonation old pressure for maintaining phonation was found to be threshold pressure (Pth), about half for that initiating it. Studies in humans, however, suggest that the extent of hysteresis may vary considerably across speakers (Plant et al., 2004), presumably for the same Bcx0kt Pth ¼ ; (1) reasons as noted above for P variation. T th It should be noted that equivalent articulatory and aero- dynamic conditions do not hold at phonation offset and onset where B ¼ tissue damping, c ¼ the mucosal wave velocity in many consonantal contexts (see Sec. IB). Even if the (which increases with vocal-fold stiffness), x0 ¼ the glottal upper vocal tract is open, as for /h/ (cf. Koenig et al., 2005), half-width, kt ¼ a transglottal pressure coefficient calculated to onset–offset differences may not reflect true hysteresis be about 1.1, and T ¼ vocal fold thickness. Subsequent mathe- effects given variations related to syllable stress. The discus- matical work has explored how Pth varies with factors such as sion will consider how onset–offset differences in the current fundamental frequency (f0), prephonatory glottal width, glottal data compare to those in classic hysteresis studies in the light convergence angle, laryngeal size, and upper vocal-tract air- of such considerations. way inertance (Chan and Titze, 2006; Lucero, 1996, 1998, 2005; Lucero and Koenig, 2005, 2007; Titze, 1992). Many studies have also assessed Pth in human speakers, B. Assumptions required for characterizing phonation evaluating effects of vocal fatigue, vocal warm-up, hydra- around voiceless obstruents and review of empirical tion, and f0 (Chang and Karnell, 2004; Elliot et al., 1995; studies Finkelhor et al., 1987; Fisher et al., 2001; Jiang et al., 1999; Several assumptions were made in obtaining the phona- Milbraith and Solomon, 2003; Motel et al., 2003; Sivasankar tion threshold formula. First, the equation holds only for et al., 2008; Solomon and DiMattia, 2000; Solomon et al., cases where the vocal folds do not contact, i.e., when the 2003, 2007; Verdolini et al., 1994, 2002; Verdolini-Marston vocal folds are slightly abducted. The obstruent environ- et al., 1990). Several papers have reported extensive individ- ments considered here involve a wide range of vocal-fold ual differences in Pth values and changes across experimen- positions (i.e., glottal widths), from adducted to widely tal manipulations (Elliot et al., 1995; Finkelhor et al., 1987; abducted. Changes in laryngeal height during voiceless con- Jiang et al., 1999; Motel et al., 2003; Solomon et al., 2007; sonants may have passive effects on vocal-fold tension (e.g., Titze, 2009). The modeling work suggests that some of this Hombert et al., 1979), and speakers may also contract the variation may reflect speaker differences in vocal-fold pa- cricothyroid muscle to actively increase longitudinal tension rameters such as glottal convergence angle, resting glottal for voiceless consonants (Hoole and Honda, 2011; Lo¨fqvist half-width, tissue viscoelasticity, and thickness of the vocal- et al., 1989). Extensions of Titze’s model have demonstrated fold body and cover (Chan et al., 1997; Chan and Titze, that higher f0, as should result from greater vocal-fold ten- 2006; Lucero, 1998). sion, increases Pth (Lucero and Koenig, 2007). Thus, multi- Although most modeling has adopted values appropriate ple laryngeal factors may inhibit